Demand apparatus.



L. T. ROBINSON.

DEMAND APPARATUS.

APPLIOATION nun MAR.18, 191s.

Patented Dec. 1, 1914.

MECHANISM Wntnesses. A4

UNITED STATES 3.5mm orrion.

LEWIS T. ROBINSON, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC I COMPANY. A CORPORATION OF NEW YORK.

DEMAND APPARATUS.

Application filed March 18,

To all whom it may concern:

Be it known that I, LEWIS T. ROBINSON, a

citizen of the United States, residing at Schenectady, county ofSchenectady, State of New York, have invented certain new and usefulImprovements in Demand Apparatus, of which the following is aspecification.

My invention relates to demand apparatus, and in particular to apparatuswhich indicate the maximum demand made by an electrical installationupon a central generating station or other source of electric energysupply.

modern problem of major importance in the distribution of electricalenergy to individual consumers is to determine the tariff rate whichshould be charged each consumer for the energy he uses. One method ofdetermining this tariff rate for electrical energy, which is regardedwith considerable favor, consists in charging the consumer at a certaincontract rate for the energy used, provided the demand does not exceed apredetermined amount. If the demand at any time exceeds thispredetermined amount, the consumer is penalized; the. amount of thepenalty depending upon the magnitude of the greatest or maximum demand.made by the consumers installation.

.This method requires for its successful operation an apparatus which-will accurately record the greatest or maximum demand made by theconsumers installation.

The object of penalizing the consumer when the demand of hisinstallation exceeds a predetermined amount is usually to induce him tomaintain his normal energy consumption or normal demand below thispredetermined amount. It is not proposed to penalize the consumer fortemporary overloads or for the effects of heavy overloads, such as shortcircuits. Accordingly it is always desirable in determining the maximumdemand tov employ as a unit of reference a period or interval which willbe just and reasonable to both the consumer and the central station.Furthermore, the inherent principle of operation of the demand apparatusshould ordinarily be such that error, if any, in the indications will bein the consurners favor and not prejudicial to him.

The primary object of my invention is to provide a demand apparatushaving the above mentioned characteristics. That is,

Specification of Letters Patent.

Patented Decfl, 1914. 1913. Serial No.755,136.

I aim to provide a novel construction of apparatus for measuring demand,and particularly maximum demand, which employs ing of this quantity ofenergy and the minimum time in which any one of a number of equalquantities of energy is metered will obviously correspond to the maximumdemand; I have employed the expression interval of metered energy todesignate a predetermined quantity of energy consumed and metered.

.- My invention then consists in measuring the time in which equalquantities or'intervals of energy aremeteredand indicating the minimumtime so measured.

In measuring and indicating the maximum demand it is often desirablethat the movement of the indicating element be directly indicative ofthedemand, so that the maximum demand will be represented by the maximummovement of the element. When the maximum demand is measured in terms ofthe timesrequired to consume predetermined and equal quantities ofenergy, the times vary inversely as the demands, and the provision of anapparatus having an indicating element Whose movement,

with reference to 'the graduatiohs on a scale, is directly indicative ofthe demand becomes a problem of considerable complexity.

An additional object of my invent-ion is, therefore, to provide a methodof and means for obtaining an indicating action-directly proportional toa variable quantity where the variable quantity is measured in a unitwhich. gives a measurement varying in mag nitude inversely as themagnitude of the quantity. In accomplishing this object of my invention,I measure the variable quantity in a unit which gives a measurementvarying inversely in magnitude as the magnitude of the quantity, andproduce'an action inversely proportional to the magni tude of themeasurement. The action so produced thus gives an indicationproportional to the variable quantity.

As applied to a maximum demand apparatus, my method consists inproducing an action inversely proportional to the time in which each ofa number of equal quantities or intervals of electrical energy ismetered and in obtaining an indication of the action of maximummagnitude so produced. It is desirable in most instances to indicate thedemand in units of energy as well as time.

A' further object of my invention is accordingly to provide a novel formof scale to be used with demand apparatus for indicating the averagerate of consumption of energy during the time a predetermined quantityof energy is consumed and metered. For this purpose I preferably providea scale having graduations to indicate time and cooperating graduationsto indicate the average rate of consumption of energy.

The novel and patentable features which I believe to be characteristicof my invention are indicated in the claims appended hereto.

The construction and mode of operation of a maximum demand apparatusembodying my invention will be understood by reference to the followingdescription taken in connection with the accompanying drawings, in whichFigure 1 is a diagrammatic view in perspective of my novel and improvedtype of maximum demand apparatus operatively connected to an electricalinstallation; Fig. 2 is a view of my novel form of scale with two formsof indicating devices; and Figs. 3, 4: and 5 are detailed views of aparticular feature of construction of the a paratus at differentinstances in the cycle 0 operations.

Referring to Fig. 1 of the drawings there is shown a substantiallyconstant speed driving mechanism 6. While I have shown a clockworkmechanism as the substantialconstant speed driving means, it will beunderstood that any othersuitable form of driving means, such as aconstant speed electric motor, may be employed. The driving mechanism 6is arranged to rotate a shaft 7'in a clockwise direction by means of apawl 8 driven directly by the mechanism and a ratchet wheel 9 rigidlysecured to the shaft 7 A cam 10 is mounted on the shaft 7 and isnormally adapted to be turned in a clockwise direction by the shaft. Theoperative con nection between the shaft and the cam is made through aspring plate 11, so that if the cam is for any reason held fixed theshaft 7 may be revolved. This flexible connection between the shaft 7and the cam 10 is a necessary feature for the successful operation ofthe apparatus.

A movable element 12 is loosely mounted on a pivoted shaft 13. A fixedstop 14 limits the movement of the element 12 in one direction anddetermines its initial or zero position. A finger 35 is rigidly securedto the shaft 13 and is arranged to contact with a pin 37 on the element12. A coil spring 36 has one end secured to the shaft 13 and the otherend secured to the pin 37, and acts to hold the finger and pin incontact. The spring is so arranged that its tension is increased whenthe pin and finger are separated. An arm 15 is secured to the elementHand is positioned to engage with some point on the periphery of the cam10 when the element 12 is moved in a clockwise di rection.

The engagement of the arm 15 with the periphery of the cam 10 limits theextent of movement of the element 12 in a clockwise direction. Theperiphery of the cam 10 is so designed that the extent of movement ofthe element 12 in a clockwise direction is a function of the anglethrough which the cam is moved from its initial position. The means fordetermining the initial position of the cam will be described more fullyhereinafter.

A lever 16 is fulcrumed about a fixed pin 17 and is operativelyconnected to the armature or plun er 18 of a solenoid 19. The lever isprovlded with a counter weight 20 which normally holds the armature inan elevated position. A link 21 operatively connects the lever 16 to asecond lever'22 pivoted on a pin 23. The lever 22 is provided with twocurved arms 24 and 25. The arm 24 is pivoted to a crank arm 26 rigidlysecured to the shaft 13. Two suitably spaced pins 27 and 28 are securedto the curved arm 25. I

A gear 29 is loosely mounted on the shaft 13 and operatively engageswith a pinion 30 rigidly secured tothe shaft 7. A ratchet wheel 31 issecured to the gear 29 and cooperates with a pawl 32 secured to a crankarm 33 loosely mounted on the shaft 13. An arm 3% is secured to orintegral with the crank arm 33 and is arranged to engage with either thepin 27 or the pm 28. Under normal conditions when the armature 18 iselevated, the arm 34' engages with the pin 28.

In Fig. 1 of the drawings I have shown my novel form of demandinstrument in combination with an induction meter. It will, of course,be understood that my invention is in no sense limited to thisparticular form of meter, but is adapted to be used -in combination withany electric meter of 7 the disk armature 38 and drives, through gearing44, the usual registering mechanism of the meter which not shown in thedrawings. The shaft 43.:1lso drives a dog 45,.

pose one terminal of the winding of the sole-' noid is connected byconductor 52 to one side of the line circuit 41 and the contact disk 49is connected by conductor 53 to the other side of the circuit 41, whilecontact member 51 is connected by conductor 54 to the other terminal ofthe winding of the solenoid.

The remaining features of the construc-- tion of my maximum demandapparatus will be best understood from a description of the operation ofthe same. The solenoid 19 is designed to be energized at the end ofequal intervals of metered energy,that is, each time that the metershaft 43 makes a prede-- termined number of revolutions. Fig. 1represents the position ofthe various elements of the apparatus a shorttime after the beginning of the metering of an interval. The contactfinger 50 has moved a slight distance in a clockwise direction from thefixed con-' tact member 51 and the cam 10 has been revolved through asmall anglefrom its initial position.

The cam 10 is revolved at substantially constant speed by theengagement. of thepawl 8 with the ratchet 9. It will be observed thatthis connection between the driving mechanism 6 and the shaft 7 preventsthe rotation of the shaft in a counter clockwise direction, but permitsa rotation of the shaft in a clockwise direction at an angular velocitygreater than the angular velocity of the pawl 8. The cam illustrated inthe. drawings is so designed that the distance through which the element12 moves before the rod 15 engages with the periphery of the cam isinversely proportional to the angle through which the cam has turnedfrom its initial position. The distance from the rod 15 to the peripheryof the cam 10 is thus inversely proportional to the length of time thecam has been rotating since start ing from its initial position.

When the predetermined quantity of energy has been metered, the contactfinger 50 engages the contact member 51, the solenoid 19 is energizedand its armature 18 is pulled down. The downward movement of thearmature 18 turns the lever 16 about its'ful- Icrum l7, and, through thecooperation of the link 21, the movable end of the lever 22 is alsomoved downwardly about its fulcrum 23. The downward movement of thelever 22 turns the crank arm 26 through a small angle in a clockwisedirection. The shaft 13 and the finger 35 are moved through a simi larangle by the movement of the arm 26.-

The tension ofthe spring 36 causes the movable element 12 to turn withthe finger 35 in ,a-clockwise direction and until the arm 15 engageswith theperipher of the cam 10. The relative posltions o the cam 10 andthe arm 15 at this instant are shown in Fig. .4 of the drawings. c.

A' non-return indicating pointer 55 is arranged to be actuated by thearm 15 and will remain in any position to which it is moved by the arm15, due to a spring plate 56 which provides a, frictional engagement ofthe pointer 55 on its shaft 57. The pointer 55 moves across a.stationary scale or record sheet 61 which is shown in greater detail in.Fig. 2.

.The angle through which the crank arm 26 is moved is sufficient toalways bring the arm 15 into engagement with the periphery of the cambefore the pin 27, which moves downwardly with the lever 22, engages thearm 34. When the pin 27 engages the arm 34, the arm 15 has movedintoengagementwith the periphery of the cam 10 and is contactingtherewith. The continued downward movement of the lever 22 causes thepin 27. to turn the arm 34 in a counter clockwise direction. As the arm34 is thus moved, the crank arm 33 carrying the pawl 32 is similarlymoved and the gear 29 is turned through a certain angle in a counterclockwise direction. The movement of the gear 29 is transmittedthroughthe pinion v30 to; the shaft 7, and since the rotation of the,

shaft thus produced is much more rapid thanj the rotation of the pawl 8,the shaft 7 and the cam 10 will turn in a clockwise direc-. pawl 8slipping over the tion with the ratchet 9.

As the cam 10 moves in a clockwise direction its periphery pushes therod 15 and the movable element 12 in a counter clockwise ture 18 isinits lowered position. When the solenoid is energized, the stop 59 isaccord-- ingly moved by the armature 18 into a position where it willarrest the cam 10. As the cam is turned by the gear 29 and the pinion30, the pin 60 engages with the stop 59,and the initial or zero positionofthe cam is thus determined. The shaft 7 is free to complete its angleof rotation due to the flexible.

connection between the shaft and the cam. The position of the cam in itsinitial position with the stop 59 engaging the pin 60 is shown in Fig.of the drawmgs. When the contact finger 50 moves out of engagement withthe contact member 51, the solenoid 19 is deenergized and the armature18 is raised by means of the counter weight 20. The shaft 13 is therebyturned in a counter clockwise direction through the cooperation of thelever .22 and the crank arm 26 until it occupies its initial or normalposition. 'The pin 28 moves up and contacts with the arm 34. The finger35 en- 15 gages with the pin 37 on the movable element 12 and completesthe return of this element to its initial position. The movement of thelever 16 upwardly moves the arm 58 in a counter clockwise direction andstop 59 is withdrawn from engagement with the pin 60. The entireapparatus has now been restored to its initial or starting position andthis cycle of operations'is repeated during each predetermined equalinterval of metered-energy.

The first effect of the rotation of the shaft 13 is to move the arm15into engagement with the periphery of the cam. The spring connectionbetween the shaft 13 and the movable element 12 permits the shaft toturn without producing a corresponding movement of the element. When thearm 15 contacts with the cam further movement of the element 12 isprevented. At the same time the shaft 13 is free to turn, and in turningwill move finger from engagement with pin 37 andwill thus increase thetensionof spring 36. The cam does not start to move to its initialposition until the arm 15 has reached the periphery of the cam, and tothis end the movement given the arm is always sufiicient to effect thisengagement before the pin 27 engages the arm 34. The second effect ofthe rotation of the shaft 13 is to .complete the revolution of the camand to bring the elements into their respective initial positions. Thegear 29 is so proportioned that the slight angular movement I given itby the pawl 32 is sufficient to turn the pinion '30 through one completerevolution, and thus the cam is always turned through one completerevolution during each interval of metered energy.

The contact finger 50 is of such a width that the finger'and contactmember 51 are, in engagement for an appreciable length of essary inorder to prevent an erroneous indication by the non-return pointer 55which is likely to result if the arm 15 is moved too rapidly.

I may use in conjunction with or in place of the non-return pointer anindicating pointer which leaves a mark on the scale showing the extentit has been moved. Such a pointer is shown in Fig. 2 of the drawings. Inthis figure, the pointer 63 is provided with a piece of marking material64 which is adapted to engage with the scale or record sheet 61. As thepointer moves over the scale it draws a line65 which indicates themaximum distance the pointer 63 has moved. The pointer 63 is preferablysecured to the arm 15 and thus moves with the movable element 12. InFig. 2 I have shown the non-return pointer 55 provided with a pin 66 inthe path of the pointer 63. In this case the pointer 55 and the line ormark 65 both indicate the maximum demand. It will be obvious that I canuse either the non-return pointer alone or the marking pointer alone. Ifthe marking pointer is used alone the friction between the record sheet61 and the marking material 64 may be made sufiicient to insure agradual movement of the pointer. In this case the dash pct may-bedispensed with and the width of the contact finger 5O considerably Ilessened.

If the substantiallyconstant speed driving mechanism 6 should stop, itis evident that the cam 10 will cease to rotate. If thisshould happensoon after the beginning of the new interval of metered energy, it isobvious that an erroneous indication might be obtained. If the meterreader, therefore, finds the mechanism 6 stopped, the indicationrecorded should be disregarded if the consumer is to be given thebenefit of the doubt. If the meter should stop, the cam 10 will continueto rotate in a clockwise direction. If the cam, completes one revolutionbefore the predetermined inter val of energy has been metered, the pin60 will engage with a stop 67 on the arm 58. This will be apparent byreference to Fig. 3. In this figure, the parts are represented in theirnormal and initial positions. When the cam 10 has made nearly onecomplete revolution, the pin 60 will be directly eneath the stop 67.Further rotation of the cam is then prevented by the engagement of thepin with the stop, but the shaft 7 continues to rotate due to theflexible connection between the shaft and the cam. When thepredetermined interval of energy has been metered, the solenoid 19 isenergized and the apparatus goes through the ereinbefore described cycleof operations.

It will be obvious by reference to Fig. 3 that the movement of the arm15 will be very small if the pin 60 is-engaged by the stop designed'toindicate units of time.

67. IThepointer' or 63,- as the case may be, will therefore, move noappreciable distance. When.the.solenoid is energized,the arm 58 ismovedas previouslydescribed, and the stop 67 moves from engagement with thepin 60, While stop 59 moves into position to engage with the stop 60When the complete revolution of the cam is completed by the gear 29 andthe pinion. 30. This position is represented in Fig. 5 of the drawings.When contact finger 50 moves'out of engagement with contact member 51,the arm 58 returns to its initial position and the cam is correctlypositioned to'again commence the cycle of operation, as indicated in F i3 of the drawings.

y demand indicator rimarily measures the time in which a pre eterminedinterval of energy is metered. This is often an undesirable unit inwhich to express the demand, and Lhave accordingly devised a novel typeof scale. Preferably this scale is provided with'two sets ofgraduations. In the form of scale illustrated in the drawings one set ofgraduations 68 are equally spaced and are Adjacent to and cooperatingwith graduations 68 are graduations 69 Which are designed to directlyindicate the avera 'e rate of consumption of energy during the time inwhich the predetermined quantity of energy is metered. The average rateof consumption of energy is indicated by ascending gradua-- tionsreading from left to right, and time is indicated by descendinggraduations reading from left to right. In the instrument illusrated,the predetermined interval of metered energy is 150 watt hours. If thisquantity of energy is metered in 60 minutes, the average rate ofconsumption of energy is 150 watts. If, however, this interval of energyis metered in 15 minutes, the average rate of consumption of energy is600 watts. This form of scale is decidedly advantageous, since itprovides a direct indication of the average rate of consumption ofenergy during a predetermined interval. It will, of course, be obviousthat where only the average rate of consumption of energy during apredetermined intervalis desired the graduations of time 68 may beomitted.

For the purpose of a maximum demand indicator, I have illustrated a cam10 which determines the extent of movement of the,

element 12 inversely as the magnitude of the angle through which the camhas moved from its initial position. It is'evident that the cam may begiven other configurations to meet certain desired conditions ofservice, and that the distance through which theelement 12 is permittedto move may be another function of the time or some function of, anotherquantity. For example, the cam may beso shaped that the movement of themovable element is-directly proportional-to the average rate ofconsumption of energy durmg the time the predetermined quantity of:energy is metered, and thus the graduations indicating average rate ofconsumption of energy Will be equally spaced.

One of the particular advantages of my maximum demand apparatus is thatit employs as a unit of reference a predetermined interval of meteredenergy. Anyerror occasioned by the failure of the apparatus to operateis inherently resolved in favor of the consumer. It will be observedthat if the apparatus fails to operate at the end of an equal intervalof metered energy the cam 10 Will continue to rotate, and thus when theapparatus does operate, probably'at the end of the next interval ofmetered energy, a longer length of time for the consumption of theenergy interval, or a lower. aver. e rate of energy consumption, will bein i cated. In no case will a failure of the instrument to operate atthe end of an energy interval give an indication of a demand whichis'prejudicial to the consumer.

' I have described and illustrated herein the best embodiment now knownto me of my invention. It will be apparent to those skilled in the artthat various changes and modifications may be made in this demandapparatus without departing from the spirit of my invention. I haveaccordingly aimed in the appended claims to cover all modificationswhich are within the scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates. is,-

1. The method of indicating the minimum time in which any one of anumber of equal quantitiesof electrical energy is consumed whichconsists in producing an action inversely proportional to the time inwhich each equal quantity of energy is consumed, and obtaining anindication of the action of maximum magnitude so produced.

2. The method of indicating the maximum demand of an electricalinstallation which consists in producing an action inverselyproportional to the time in Which each of a number of equal quantitiesof electrical enmoving said member a distance inversely proportional tothe time in which a prede tel-mined quantity of electrical energy isconsumed, and means for indicating the maximum movement of said memberduring any one of a number of its movement in response to the lastmentioned means.

5. An apparatus for indicating the demand of an electrical installationcomprising a movable member,'means for producing a movement of saidmember indicative of the time required. to consume a predeterminedquantity of electrical energy, and means operatively related to saidmember and adapted to indicate the extent of movement of the member.

6. A demand apparatus comprising in combination an electric meter, amovable element, means for moving said element a distancewhich is afunction of the time in which a (predetermined quantity of energy ismetere and means cooperating with said element for directly indicatingtie average rate of consumption of energy during said time.

7. A demand apparatus comprising in combination an electric meter, amovable element, means for moving said element a distance which is afunction of the time in which a predetermined quantity of energy ismetered. and means cooperating with said element for indicating the timein which said quantity of energy is metered.

8. A demand apparatus comprising in combination an electric meter, amovable element, means for moving said element a distance which is afunction of the time in which a predetermined quantity of electricalenergy is metered, and means for indicating by the position of saidelement the average rate of consumption of energy during said time.

9. A demand apparatus comprising in combination an electric meter, amovable element, means for moving saideleme'nt a distance which is afunctionof the time in which a predetermined quantity of electricalenergy is metered and for returning said element to an initial positionafter said quantity of energy is metered. and means for causing saidelement to leave an indication of the minimum time in which any one of anumber of equal quantities of energy each equal to said predeterminedquantity is metered.

10. A demand apparatus comprising in combination an electric meter, amovable element, means for moving said element a distance which is afunction of the time in which a predetermined quantity of energy ismetered. and means cooperating with said element for obtaining anindication of the minimum time in which any one of a number of equalquantities of energy each equal to said predetermined quantity ismetered.

11. A demand apparatus comprising in combination an electric meter, amovableelement, means for moving said element a distance which is afunction of the time in which a predetermined interval of energy ismetered, and means cooperating with said element for indicating themaximum average rate of consumption of energy during any one of a numberof intervals of energy each equal to said predetermined interval.

12. A demand apparatus comprising in combination an electric meter, amovable element, means for producing a movement of said elementinversely proportional to the time in which a predetermined quantity ofelectrical energy is metered, and means cooperating with said elementfor indicating the average rate of consumption of energy during saidtime.

13. A demand apparatus comprising in combination an electric meter, ascale having graduations to indicate the average rate of consumptionofcnergy during the time a predetermined quantity of energy is metered,a movable element arranged to sweep across said scale, and means formoving said element a distance indicative of the average rate ofconsumption of energy during said time.

14. A demand apparatus comprising in combination an electric meter, amovable element, means for producing a movement of said elementinversely proportional to the time in which a predetermined quantity ofelectrical energy is metered, and means in operative relation with saidelement for indicatina the time in which said quantity of energy ismetered.

15. A demand apparatus comprising in combination an electric meter. amovable element having an initial position, means for producing amovement of said element inversely proportional to the time in which apredetermined quantity o1 electrical ener y is metered and for thenreturning the element to its initial position, means in onera= tiverelation with saidelement for indicating the time in which said quantityof energy is metered, and means for indicating the maximum movement ofsaid element produced during the metering of a number of equalquantities of energy each quantity equal to said predetermined quantity.

16. A demand apparatus comprising in combination an electric meter. amovable element having an initial position, and means controlled by saidmeter and actuated at equal intervals of metered energy for movinc: saidelement a distance indicative of the average rate of consumption ofenergy during the interval and for then returning the element to itsinitial position.

'17. A demand apparatus comprising in combination an electric meter. amovable element having an initial position, means controlled by saidmeter and actuated at equal intervals of metered energy for moving saidelement a distance indicative of the average rate of consumption ofenergy during the interval and for then returning the element to itsinitial osition, and means for indicating the maximum movement of saidelement.

'18. A demand apparatus comprising in combination an electric meter, amovable element having an initial position, and means for producing amovement of said element indicative of the average rate of consumptionof energy during a predetermined interval of metered energy and forreturning said element to its initial position aftersuch movement hasbeen produced.

19. A demand apparatus comprising in combination an electric meter, amovable element having an initial position, means for producing amovement of said element indicative of the average rate of consumptionof energy during a predetermined interval of metered energy and forreturning said element to its initial position after such movement hasbeen produced, and means cooperating with said element for indicatingthemaximum rate of consumption of energy during any one of a number ofintervals of energy each equal to said predetermined interval.

20. A demand apparatus comprising in combination an electric meter, amovable element, at time actuated cam arranged to limit the movement ofsaid element in one direction, means controlled by said meter andactuated at equal intervals of metered energy for moving said elementinto engagement with said cam and for returning the cam and the elementto their respective initial positions, and means cooperating with saidelement for indicating the minimum time in which any one of the equalintervals of energy is metered.

21. A demand apparatus comprising in combination an electric meter, amovable element having an initial position, a time actuated cam havingan initial position and arranged to determine the extent of movement ofsaid element in one direction as a function of the angle through whichthe cam has moved from its initial position, and

means controlled by said meter and actuated at equal intervals ofmetered energy for moving said element into engagement with said cam andfor returning the cam and the element to their respective initialpositions.

22. A demand a aratus comprising in combination an electric meter, amovable element having an initial position, a time actuated cam havingan initial position and arranged to determine the extent of movement ofsaid element in one direction inversely as the magnitude of the anglethrough which the cam has moved from its initial position,

and means controlled by said meter and actuated at equal intervals ofmetered energy for moving said element into engagement with said cam andfor returning the cam and the element to their-respective initialpositions.

239A demand apparatus comprising in combination an electric meter, amovable element having an initial position, a time actuated cam havingan initial position and arranged to determine the extent of movement ofsaid element in one direction as the function of the angle through whichthe cam has moved from its initial position, means controlled by saidmeter and actuated at equal intervals of metered energy for moving saidelement into engagement with said cam and for returning the element andthe cam to their respective initial positions, and means for indicatingthe maximum movement of said element.

24. A demand apparatus comprising in combination an electric meter, amovable element having an initial position, a time actuated cam havingan initial posi'tion andarranged to determine the extent of movement ofsaid element in one direction inversel as the magnitude of the anglethrough w ich the cam has moved from its initial position,

